This invention relates to a process for the preparation of N-substituted acrylamides. More particularly it relates to an improved process for the preparation of N-substituted acrylamides of the general formula CH2xe2x95x90CHxe2x80x94CONHR, wherein, R is alkyl group having carbon 1 to 22 or acyl group having carbon 1 to 18 by Friedel-Craft""s alkylation and acylation of acrylamide respectively, in the presence of a Lewis acid catalyst.
Copolymers of N-alkylacrylamides with various other monomers are finding diverse applications as follows:
1) Poly (xcex2 napthyl 6 acrylamidocaproate-co-acrylic acid) as plant growth regulator (C.J. Boundreaux, W. C. Bunyard and C. L. Mccormick, J. Controlled Rel. 40,223 (1996).
2) Poly (N-dodecylacrylamide-co-N-methyl 4vinyl pyridinium Na) as salt resistant viscosity builder (D. Christine, B. Alain and L. Pierre, Macromol. Symp. 102,233 (1995), D. Christine, B. Alain, B. Fransis and V. M. Laure, Polymer 36,2095 (1995).
3) Poly (N-stearoyl acrylamide-co-2(3-acrylamidopropyl) dimethyl aminoethyl isoproply phosphate) as phosphatidylcholine analogous material (W. Yenfeng, C. Tianming, K. Masaya and N. Taiao, J. Polym. Sci. Chem. Edn. 34,449 (1996).
4) Poly (N-tert-octylacrylamide-co-N-alkylacrylamide) as thickner in cosmetics (J. Mondet and B. Lion Eur. Pat. Appl. EP 494,022.
5) Poly (N-octylacrylamide-co-3 acrylamido-3 methyl butanoate Na) for oil recovery (A. Kitagawa and T. Koichi, Jpn. Kokai Tokkyo Koho JP 07,188,347) and so on.
Crosslinked hydrogels based on N-alkylacrylamides also find various applications such as thermosensetive polymeric drug carriers (C. L. Mecormick and J. C. Brent, Polym. Mater. Sci. Eng. 55,366 (1986), M. Akashi, A. Kishida, S. Sakuma and H. Kikuchi, PCT Int. Appln. WO 9730730. H. Yu and D. W. Grainger, Polym. Prepr. 34,820 (1993), materials for hard contact lenses (S. Q. Zhou, L. Xiugao and Y. Wang PCT Intl. Appln. WO 9735,896), concentration of aqueous protein solutions (J. Manrong. Z. Guiying, W. Changfa, L. Peiyi and H. Wei, Gaofenzi Xubao 3, 321 (1995), Stationary phases for HPLC ((N. Shoji, I. Hirotaka and H. Chuichi, Polymer J. (Tokkyo 25, 609 (1993)) etc.
In order to meet these growing demands of N-alkylacrylamides. various methods for their synthesis have been developed. These methods can broadly be classified into three types viz.
1) Reaction of acryloyl chloride with alkyl amine,
2) Pyrolysis or thermal decomposition of carboxylic acid amides, and
3) Reaction of olefins with nitriles.
The above mentioned processes are described in brief hereinbelow:
Methods of Type 1
Reaction of Acryloyl Chloride with Alkylamine
In this method N-alkylacrylamides are synthesized by reacting acryloyl chloride with alkyl amines in the presence of acid quencher i.e. triethyl amine at 0xc2x0 C. (C. G. Overberger, C. Frazier and J. Mandehman, J. Am. Chem. Soc. 75,3326 (1953), J. Lal and G. S. Trick, J. Polym. Sci. A2, 4559 (1964), E. F. Jr. Jordan, G. R. Riser and B. Artymyshyn, J. Appl. Polym. Sci. 13,1777 (1969), K. J. Shea, G. J. Stoddard, D. M. Shavelle, F. Wakui and R. M. Chaote, Macromolecules 23,4497 (1990).
Methods of Type 2
Thermal Decomposition of Carboxylic Acid Amides.
A number of patents which are based on this technique have been filed. A Japanese patent No. Jpn. Kokai Tokkyo JP 07,145122, discloses the synthesis of N,N diethylacrylamide as follows. Methyl acrylate was reacted with diethylamine to give Michael addition product methyl xcex2 N,N diethylaminopropionate. This was treated with sodium methoxide for 46 hrs and then with phosphoric acid for 1 hr. at 50xc2x0 C. to give N,N diethyl xcex2 diethylaminopropionic acid amide which was then thermally decomposed at 180xc2x0 C. and 100 torr pressure for 4 hrs. to give N,N diethylacrylamide (K. Motomasu, I. Seiichi and I. Massasane, Jpn. Kokai Tokkyo Koho JP 07,145 122). Similar process for the synthesis of N,N dialkyl acryl and methacrylamides has been reported wherein, thermal decomposition of carboxylic acid amide was carried out in the presence of H2SO4 at 195xc2x0 C. (T. Maruyama, 0. Kido, I. Okidaka and R. Hiraoka, Jpn. Kokai Tokkyo Koho JP 04,208 258).
N-alkylacrylamides have also been synthesized by amidation of bicyclic carboxylic acids followed by the thermal decomposition of the carboxamide. Thus N,N dimethylacrylamide was synthesized by reacting dimethylamine with bicyclo [2.2.1]hept-2-ene-2-carboxylic acid in autoclave to give N,N dimethyl bicyclo [2.2.1]hept-2ene-2-carboxylic acid in autoclave to give N,N dimethyl bicyclo [2.2.1]hept-2-ene-2-carboxamide, followed by its thermal decomposition at 200xc2x0 C. in vacuo (A. Ohshima and K. Tsubashima Jpn. Tokkyo Koho 7909 170, A. Oshima, K. Tsubashima and N. Takahashi Ger. Offen. 2,217,623). The use of pyrolysis for preparation of N-alkylacrylamides has also been reported. In this, N(1,1 dimethyl 1-3 oxybutyl)-3 methoxy propionamide was hydrogenated in the presence of dimethylamine p-toluenesulfonic acid and Pt. catalyst to give N(1,1 dimethyl -3 dimethyl aminobutyl) 3 methoxy propionamide. This was heated with NaOH at 80 to 90xc2x0 C. for 3 hrs to give N(1,1dimethyl-3 dimethylaminobutyl) acrylamide (D. I. Hoke, U.S. Pat. No. 3,943,114).
Methods of Type 3
Reaction of Olefins with Nitriles
N-alkylacrylamides have also been synthesized by reacting acryloni{acute over (t)}rile with various olefins. A Japanese patent No. Japan Kokai 7391011 discloses the synthesis of N-tert-octylacrylamide by reacting acrylonitrile with 2,4,4 trimethyl 1-pentene at 40xc2x0 C. for 3 hrs using 65% H2SO4 as solvent (T. Takada, Y. Kawakatsu, T. Mihamisawa and K. Hara, Japan Kokai-7391011). Similarly, acrylonitrile has been reacted with dimethylamine at 200xc2x0 C. in the presence of Lewis acid ZnCl2 to give N,N dimethylacrylamide (Asahi Chemical Ind. Co. Ltd. Fr. 2,046 122). N-alkylacrylamide has also been synthesized by oxidative carbonylation. In this, PdCl2, CuCl2, CuCl and propylamine in 1:10:10:120 ratio were treated with methane, carbon monoxide and oxygen to give N-propylacrylamide (G. Biale U.S. Pat. No. 3,523,971).
Amongst the above sighted processes for preparation of alkylacrylamides, methods of the type 1) cannot be used to synthesize N-acylacrylamides, monomers, that are gaining increasing importance. Besides, it is also not attractive for large scale productions since it uses acryloyl chloride which is an expensive and hazardous reagent.
Other processes sighted for the preparation of alkylacrylamides i.e. methods of type 2) and 3) suffer from the drawbacks of harsh reaction condition such as high temperatures, high vacuum and tedious work up procedures. Also in most of the cases N-alkylacrylamide with small alkyl chain length were synthesized.
It is therefore an object of the present invention to provide process for the preparation of N-substituted acrylamides.
Another object of the present invention is to provide a process with mild reaction conditions such as reaction at room temperature and atmospheric (normal) pressure which will obviate tedious work up procedures used in the conventional processes.
It is also an object of the present invention that such a process be applicable for the preparation of N-substituted acrylamides with long alkyl chain length.
Friedel-Craft""s alkylation is an effective and convenient method which is widely used to synthesize linear alkyl benzenes (LABs). Despite this, its use in the synthesis of N-alkylacrylamides has not been reported yet. It has now been found that N-alkylacrylamides and N-acylacrylamides can be produced in high yields by alkylation and acylation of acrylamide respectively, in the presence of a Lewis acid catalyst in suitable solvent at room temperature and atmospheric pressure.
Accordingly the present invention provides an improved process for the preparation of N-substituted acrylamides of the general formula CH2xe2x95x90CHxe2x80x94CONHR wherein, R is alkyl group having carbon 1 to 22 or R is acyl group having carbon 1 to 18 which comprises reacting acrylamide with alkyl/acyl chloride in the presence of a Lewis acid catalyst in an organic solvent at a temperature ranging between room temperature to 50xc2x0 C. for a period ranging between 1 hour to 24 hours, terminating the reaction if necessary and cooling to ambient temperature, pouring the mixture in a non-solvent to obtain the precipitated product-N-substituted acrylamide.
In one of the embodiment of the present invention acrylamide used may be such as compounds of the formula CH2xe2x95x90CRxe2x80x94CONH2, wherein, R is hydrogen or methyl.
In another embodiment alkyl chloride used may be such as compounds of the formula CH3xe2x80x94(CH2)n-Cl, wherein, n is an integer from 0 to 21 and the alkyl chloride may be prepared by treating corresponding alcohol with thionyl chloride.
In yet another embodiment acyl chloride used may be such as compounds of the formula CH3xe2x80x94(CH2)n-COCl, wherein, n is an integer from 0 to 16 and the acyl chloride may be prepared by treating corresponding acid with thionyl chloride.
In still another embodiment Lewis acid catalyst used may be metal chlorides such as aluminium chloride, zinc chloride, nickel chloride.
In an another embodiment the solvent used may be such as acetonitrile, tetrahydrofuran, acetone, nitrobenzene, dioxane.
In an another embodiment the non-solvent used may be such as water, hexane, diethyl ether.
In a feature of the present invention, the process is typically carried out under mild conditions. Stoichiometric amounts of acrylamide and alkyl chloride or acyl chloride are dissolved in a suitable solvent and the stoichiometric amount of a Lewis acid catalyst is added and the reaction mixture is stirred at room temperature for 5 to 10 minutes. This is followed by vigorous evolution of hydrogen chloride gas formed due to N-alkylation or N-acylation of acrylamide. Reaction is exothermic which increases the temperature of reaction mixture from room temperature to 40 to 50xc2x0 C. After the evolution of hydrogen chloride ceases, the reaction mixture is cooled down to room temperature and poured into another solvent which is a nonsolvent for the product i.e. N-substituted acrylamide Precipitated N-substituted acrylamide is then isolated.
The ranges and limitations provided in the instant specification and claims are those which are believed to particularly point out and distinctly claim the present invention. It is however understood that other ranges and limitations which perform substantially the same function in the same or substantially the same manner to obtain the same or substantially the same results are intended to be within the scope of the instant invention as defined by the instant specification and claims.